The present invention concerns an internal combustion engine with an air separator for the separation of intake air of a composition that, in comparison to normal, is enriched with an oxygen-rich permeate and a nitrogen-rich retentate, and a method for realizing such an internal combustion engine.
An internal combustion engine which can be fed with nitrogen- or oxygen-enriched intake air is known from U.S. Pat. No. 6,173,567 B1. The process of enriching the intake air takes place via the respective air accessories and a membrane separator, which is capable of providing two air supplies, one enriched with the oxygen-rich permeate, the other with the nitrogen-rich retentate. The use of an internal combustion engine alternatively enriched with oxygen-rich and nitrogen-rich intake air enables the reduction of pollutants formed within the engine. Enriching the intake air with nitrogen lowers the combustion temperatures, which leads to a decrease in nitric oxide formation within the combustion space of the internal combustion engine. Enrichment of the intake air reduces soot particle formation within the engine. The amount by which pollutant emissions from the internal combustion engine is reduced, however, is highly dependent on the degree of retentate and/or permeate enrichment and therefore on the separation capacity of the air separation unit. In addition, it is essential that the air separation membrane have a high degree of durability in order to achieve a reliable decrease in pollutant emissions over the lifespan of the internal combustion engine. Considering efficiency requirements in general, it is also desirable to keep additional expenditures to a minimum while demanding as little installation space as possible.
An object of the invention, therefore, is to provide an internal combustion engine with an air separation unit, and a method of realizing such an engine, which can attain improved reliability, increased air separation capacity, and a greater reduction of pollutant emissions.
This object can be achieved by having the air separation unit connected to the outlet of the charged air cooler so that, during operation of the engine, at least one of fluid contents and solid contents is removable from compressed intake air coming from the charging unit during a purification stage before feeding the compressed intake air into the air separation unit.
The internal combustion engine, preferably of diesel engine design, is equipped with a charging unit, for example an exhaust-driven turbo-charger, for the compression of intake air, and a charged air cooler for the cooling of compressed intake air. An air separation unit is envisioned for separating at least a portion of the compressed intake air into a composition that, in comparison to normal, is enriched with an oxygen-rich permeate and a nitrogen-rich retentate. Thus, one or several cylinders of the internal combustion engine can at least periodically be fed with the retentate enriched by the air separation unit. In accordance with the invention, the charged air cooler is connected to the outlet of the charging unit.
The air separator is preferably realized using a membrane separation unit of common design. Employment of a different type of air separation unit, for example one based on the Ranque-Hilsch effect, is also possible. Regardless of the type of air separation unit, the oxygen-enriched outlet air flow will be designated here as the permeate, and the nitrogen-enriched outlet air flow will be designated as the retentate. For the purposes of simplicity, the supply of the permeate and the retentate will in the future be designated as the separated air.
Employment of a comparatively highly nitrogen-enriched retentate is naturally desirable for the reduction of nitric oxide formation within the engine. Given a great enough enrichment, use of exhaust air recycling can if necessary be omitted, resulting in associated cost advantages and a reduction of installation space. The separation capacity of conventional air separation units, however, is heavily dependent on service conditions like working pressure and air flow rate. A rise in air flow rate results in a loss of separation capacity, i.e., the degree of permeate and retentate enrichment as related to the design volume of the air separation unit.
The additional pressure necessary for air separation is accomplished with a charging unit, typically the compressor unit of a turbo-charger installed at the intake side of the air separation unit. If necessary, an additional compression unit can be included. A significant improvement in a high separation capacity of the air separation unit will be occur with a configuration using a charged air cooler according to the invention. One aspect of this concerns the general increase in separation capacity with lower air temperatures; another aspect is that, due to cooling of the compressed air flow, the volumetric air flow is reduced in accordance with the basic gas laws. Therefore, a greatly improved separation capacity can be achieved with the addition of a cooled air flow. As the result of reduced thermal demands, the life expectancy of the air separation unit is increased.
According to the invention, a purification unit may be provided in the circulation path between the charged air cooler and the air separation unit for purification of supplied air. In this way, the air separation unit can be kept free of contaminants, which would otherwise interfere with separation capacity over time. The life expectancy and reliability of the air separation unit will thus be significantly improved.
The purification unit may be designed for removal of fluid and/or solid contents from the air supply. The air fed to the air separation unit can contain contaminants as the direct result of compression. For instance, compressor oil loss can often allow very finely distributed oil droplets to enter the compressed air as contaminants. These will be removed by separation inside the purification unit. To be able also to remove condensed water, the provision of a fluid separator is advantageous. Solid contents will be preferably removed with a fine filter.
One or several cylinders of the internal combustion engine can be at least periodically fed with permeate provided by the air separation unit. The addition of oxygen-enriched intake air will improve combustion within the respective cylinder. This is especially effective in confronting soot formation. The permeate can thus be either mixed with the regular intake air or fed separately.
A compressor unit for the permeate provided by the air separation unit may be used for the supply of at least one cylinder of the internal combustion engine, whereas a separate intake valve is envisioned for each respective engine cylinder or respective cylinders being fed by the permeate. The oxygen-enriched permeate will in this embodiment be compressed to an appropriate pressure that is significantly greater than the peak cylinder pressure and its injection into the combustion chamber through the separate intake valves preferably synchronized. Preferable injection can optimize the soot-reducing effect of adding the permeate.
An air separation unit of the invention may have multiple air separation modules. The separation capacity of the air separation unit can be varied via an adjustable air supplier for the air separation modules. In this way, the amount of air being fed through the air separation unit can conform to varying requirements. In the event that a high enrichment of the intake air with retentate is anticipated, for example, selector valves will send intake air to all available air separation modules in order to achieve the maximum separation capacity. Alternatively, selector elements will enable some or all of the separation modules to be removed from the intake air flow. In the latter case, the air separation unit will be bypassed.
An exhaust gas purification unit, in particular an exhaust particle filter, can be provided with permeate from the internal combustion engine's air separation unit. Instead of ejecting the permeate provided by the air separation unit into the surrounding atmosphere, it can be directed to the exhaust system and there used to advantage in exhaust gas purification. In this way, soot burn-off from a particle filter can for instance be assisted, or other oxidizing exhaust gas purification functions supported.
In a method according to the invention, the internal combustion engine will be equipped with a charging unit that compresses intake air, which is then directed into an air separation unit. The air separation unit makes available intake air of a composition that, in comparison to normal, is enriched with an oxygen-rich permeate and a nitrogen-rich retentate. One or several cylinders of the internal combustion engine will at least periodically be fed with the retentate provided by the air separation unit, whereas the intake air compressed by the charger unit undergoes a purification stage prior to entering the air separation unit which involves the removal of fluid and/or solid contents. A method according to the invention enables a combustion process with reduced nitric oxide formation via the addition of intake air that possesses an oxygen content lower in comparison to normal atmospheric air. The long service life and idle periods required of the air separation unit, particularly in motor vehicles with high mileage, will be achieved by purifying the intake air entering the air separation unit. The purification act or step is preferably accomplished by thoroughly removing as many fluid and solid contents as possible from the intake air directly prior to its entry into the air separation unit. An appropriate filter unit or separator can be envisioned for this purpose. This enables the use of sensitive air separation materials, which can result in corresponding cost advantages.
An embodiment of the method presents the option of adding either all of the intake air compressed by the charging unit or only a limited portion of that intake air into the air separation unit. Flow selection devices like shut-off valves or flow dividers preferably adjust the portion of air entering air separation unit. It can be advantageous if only a limited nitrogen enrichment takes place, especially during partial or low engine loads. The portion of intake air that is to undergo separation can for instance be determined with a load-r.p.m. engine map. An optimal separation of the intake air can thus be attained.
Re-compressed permeate provided by the air separation unit can be added into at least one of the cylinders of the internal combustion engine after the peak of combustion and at a pressure greater than the peak cylinder pressure. Soot formation in particular will be suppressed by the increased oxygen content. Since the addition of the permeate takes place as the combustion is dying off, an increase in nitric oxide formation in the combustion chamber will be avoided, particularly when the subsequent addition of intake air is to be enriched with nitrogen. In this manner both soot emissions and nitric oxide emissions can be diminished. It is especially advantageous that the permeate is being blown into the cylinder at a pressure as high as or higher than approximately twice the pressure inside the cylinder. The resulting turbulence is especially effective at improving the oxidation of soot-forming nuclei, so that an especially effective reduction of soot emission can be achieved.
The permeate provided by the air separation unit can be combined with a regeneration process for a particle filter installed in the exhaust system of the internal combustion engine. The permeate will be fed into the exhaust system upstream from the particle filter. The increased oxygen content of the exhaust will improve the soot burn-off from the particle filter, thus keeping the exhaust temperature increase necessary for particle filter regeneration comparatively low. This significantly assists the process of particle filter regeneration.
Advantageous embodiments of the invention are illustrated in the drawing figures and will subsequently be described. Both the features previously referred to as well as those to be subsequently explained are thus applicable not only in the respectively described combinations but also in other combinations, as well as uniquely, without departing from the framework of the invention at hand.